1. Field of the Invention
The present invention relates to an apparatus for the collection of dust from a gaseous stream, and particularly, low pressure pulsed cleaning of filter bags in a bag collection gas filtration system. In particular, the present invention relates to a cleaning system for dislodging dust from a high capacity gas stream filter, said filter having a dirty gas plenum contiguous with a clean gas plenum, said clean gas plenum and dirty gas plenum being separated by an intermediate tube sheet having therein an array of openings, such that said tube sheet may be viewed as having a plurality of pie-shaped radial segments, with each such radial segment having a fixed array of openings, which array may vary from one radial segment to another, but which array contains substantially the same number of openings in approximately the same positions as the openings of each other radial segment, and employing gas-permeable filter media having mouths communicating with said clean gas plenum, demountably attached to said openings in said intermediate tube sheet and extending into the space defined by said dirty gas plenum, for the collection of dust, which cleaning system comprises:
a cleaning gas supply means external to said gas stream filter for supplying a quantity of pressurized gas; PA1 a pressurized gas distribution arm within said clean gas plenum and spanning a pie-shaped segment of said tube sheet extending radially between approximately the center position and approximately the outer edge of said clean gas plenum, said arm being in fluid communication with said external gas supply means, and being rotatable about said center position; PA1 a plurality of filter elements, each said element comprising: PA1 a plurality of outlet orifices in fluid communication with said external gas tank, and positioned on the side of said arm facing said tube sheet, a sufficient quantity of said orifices being present to communicate with the all of said filter elements in each radial segment; PA1 a drive means capable of rotating said arm about said center position, bringing the orifices of said arm into alignment with the filter elements of each radial segment in a sequential manner; and, PA1 control means capable of releasing a controlled low pressure pulse of gas from said external tank, through said plurality of orifices, into the venturi nozzles of said filter elements, as the orifices of said arm are positioned over the filter elements of a radial segment. PA1 a cleaning gas supply means external to said gas stream filter for supplying a quantity of pressurized gas; PA1 a pressurized gas distribution arm within said clean gas plenum and spanning a pie-shaped segment of said tube sheet extending radially between approximately the center position and approximately the outer edge of said clean gas plenum, said arm being in fluid communication with said external gas supply means, and being rotatable about said center position; PA1 a plurality of filter elements, each said element comprising: PA1 a plurality of outlet orifices in fluid communication with said external gas tank, and positioned on the side of said arm facing said tube sheet, a sufficient quantity of said orifices being present to communicate with the all of said filter elements in each radial segment; PA1 a drive means capable of rotating said arm about said center position, bringing the orifices of said arm into alignment with the filter elements of each radial segment in a sequential manner; and, PA1 control means capable of releasing a controlled low pressure pulse of gas from said external tank, through said plurality of orifices, into the venturi nozzles of said filter elements, as the orifices of said arm are positioned over the filter elements of a radial segment.
an opening in said intermediate tube sheet; PA2 a filter medium, such as a gas-permeable bag, demountably attached to said opening, and extending into the space defined by said dirty gas plenum from said opening, and having a mouth communicating with said clean gas plenum; and, PA2 a venturi nozzle positioned centrally within said mouth; PA2 an opening in said intermediate tube sheet; PA2 a filter medium, such as a gas-permeable bag, demountably attached to said opening, and extending into the space defined by said dirty gas plenum from said opening, and having a mouth communicating with said clean gas plenum; and, PA2 a venturi nozzle positioned centrally within said mouth;
2. Description of Related Art
Gas stream filtration has been known for many years, and one popular method of providing such filtration is to pass the dust-laden gas, such as air from an industrial process, from a dirty gas plenum to a clean gas plenum through a filtration media. One of the most common of such media are gas permeable natural or synthetic cloth bags, although porous foam or pleated filter media cartridges or metallic mesh tubes are known or suggested for this use as well, which are hung from openings in the partition, or tube sheet, between the two plenums. Gas passes through the porous surface of the cloth bag, but the dust and any particulate material is trapped on the outside surface of the bag.
As the filter is employed, however, dust building up on the outside surface of the filter media elements reduces efficiency and would eventually render the filter inoperative. Various systems have been proposed to deal with such dust and particulate materials. In general, the systems have comprised back-flushing the filter media with a pulse of gas, and various references have dealt with the supply of such back-flushing gas into the filter media. It would, for example, be possible to periodically pressurize the clean gas plenum, or de-pressurize the dirty gas plenum, causing a back-flow of gas reversibly through the filter media. This would however, require an enormous volume of gas and would take the entire filter off-line for the time required.
One solution which has found favor has been to include a traveling arm or bar in the clean air plenum which is connected to orifices over the filter elements. This arm or bar typically revolves above the tube sheet from which the filter media depend. In earlier versions of these kind of apparatus, a constant volume of gas was discharged from these orifices, which back-flushed the cleaning elements as the orifices passed over the filter elements. Later versions of this technology attempted to pulse the flow of cleaning gas only when the orifices were in position over the filter elements.
One problem with such an apparatus, however, is the volume of gas required to perform this function. Constant gas supply systems required an enormous gas supply, and intermittent supply systems, while they required less, involved more complicated mechanical systems. In addition, the pressure drop from the pressurized gas source, such as a gas accumulation tank, to the orifices exacerbated the problem. In order to reduce the volume of gas required, many systems placed a gas accumulator tank within the clean air plenum, reducing the length of the gas supply assembly. While this was an adequate solution for many purposes, the presence of an accumulator tank and its complicated electrical and mechanical systems limited the applications of this technology to environments which were not destructive of the equipment.
Movement of the cleaning gas supply outside the clean air plenum, however, increased the systemic pressure drop, and required significantly higher pressure systems to be operative.
U.S. Pat. No. 3,487,609 to Caplan is entitled METHOD AND APPARATUS FOR FILTERING A GASEOUS MEDIUM. This reference shows a system for cleaning filter bag elements in which a positive reverse flow of clean gas is directed into the outlet of each filter bag.
U.S. Pat. No. 3,543,481 to Pausch is entitled HIGH PRESSURE CLEANING OF DUST SEPARATING APPARATUS. This reference shows a method and apparatus for dislodging dust from a porous filtering surface, embodying the use of high pressure gas emitted from a reservoir in such a manner as to impart a high pressure shock to one or more porous filtering surfaces to dislodge heavily compacted solids therefrom.
U.S. Pat. No. 3,648,442 to Bourne is entitled DUST COLLECTORS. This reference shows a filtering system in which trapped dust is dislodged by reversing the flow of air through the bag walls sequentially. The dust which then falls to the floor of the dirty air plenum is then swept toward an exhaust port and discharged.
U.S. Pat. No. 3,832,832 to Hoon is entitled METHOD AND APPARATUS FOR CLEANING THE FILTER ELEMENTS OF A DUST COLLECTOR. This reference shows a bag type filtration system in which the filter elements are periodically cleaned by reversing the direction of air flow and immediately restoring the normal air flow within a period of a fraction of a second.
U.S. Pat. No. 3,951,627 to Barr and Mullinax is entitled AIR FILTERING APPARATUS. This reference shows a filtering apparatus providing intermittent reverse flow to dislodge accumulated material.
U.S. Pat. No. 4,157,899 to Wheaton is entitled PULSED BACKFLUSH AIR FILTER. This reference shows a cleaning system for sleeve-type air filters in which a rotating arm is periodically supplied with pulsed air at pressure to randomly backflush the sleeves.
U.S. Pat. No. 4,233,041 to Noland is entitled BAGHOUSE WITH ROTATING SWEEP ARM. This reference shows a cleaning arm for a cylindrical baghouse pivoting centrally within the clean air plenum with a cam controlled valve to provide backflushing air to successive concentric rings of filter bags with each full revolution of the cleaning arm.
U.S. Pat. No. 4,306,890 to Gustavsson and Valli is entitled APPARATUS FOR CLEANING OF FILTER ELEMENTS. This reference shows an apparatus for cleaning filter cells grouped around a common center with a pulse of compressed air. A gooseneck shaped duct rotates about a central axis and pulses compressed air when it is centered over a filter elements.
U.S. Pat. No. 4,539,025 to Ciliberti and Lippert is entitled FILTERING SYSTEM. This reference shows a filter system in which a cylindrical shell is provided with a central filter tube. This arrangement may be subjected to a periodic backflush with a jet pulse intended to flex the filter tube and dislodge collected solids.
U.S. Pat. No. 4,544,389 to Howeth is entitled MULTIPLE JET BACKFLUSHED AIR FILTER. This reference shows a porous media type air filter unit having a multiple jet reverse flow cleaning system for the filter element wherein a substantial volume of jet cleaning air and entrained ambient air are used to flush the filter element to remove accumulated dust particles.
U.S. Pat. No. 4,655,799 to Bosworth, Adams and Wheaton is entitled PULSE CLEANING SYSTEM FOR DUST FILTERS. This reference shows a cleaning system for dislodging dust from the filter bags of a dust filtration system in which the tube sheet from which the bags depend is divided into segments having filter bag openings arranged in the same pattern. A revolving air-accumulator tank is supplied with compressed air is contained within the clean air plenum and connected with a distribution arm which supplies air pulses to the filter bags through an array of discharge nozzles arranged in the same pattern as the filter bag openings.